/*
 * Copyright (C) 1997-2001 Id Software, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 * 02111-1307, USA.
 *
 * =======================================================================
 *
 * Quake IIs legendary physic engine.
 *
 * =======================================================================
 */ 
 

#include "header/local.h"

#define STOP_EPSILON 0.1
#define MAX_CLIP_PLANES 5
#define STOPSPEED 100
#define FRICTION 6
#define WATERFRICTION 1

/*
 * pushmove objects do not obey gravity, and do not interact
 * with each other or trigger fields, but block normal movement
 * and push normal objects when they move.
 *
 * onground is set for toss objects when they come to a complete
 * rest. It is set for steping or walking objects.
 *
 * doors, plats, etc are SOLID_BSP, and MOVETYPE_PUSH
 * bonus items are SOLID_TRIGGER touch, and MOVETYPE_TOSS
 * corpses are SOLID_NOT and MOVETYPE_TOSS
 * crates are SOLID_BBOX and MOVETYPE_TOSS
 * walking monsters are SOLID_SLIDEBOX and MOVETYPE_STEP
 * flying/floating monsters are SOLID_SLIDEBOX and MOVETYPE_FLY
 *
 * solid_edge items only clip against bsp models.
 */

edict_t *
SV_TestEntityPosition(edict_t *ent)
{   
	if (!ent)
	{
		return NULL;
	}
     
	trace_t trace;
	int mask;

	if (ent->clipmask)
	{
		mask = ent->clipmask;
	}
	else
	{
		mask = MASK_SOLID;
	}

	trace = gi.trace(ent->s.origin, ent->mins, ent->maxs,
			ent->s.origin, ent, mask);

	if (trace.startsolid)
	{
        if ((ent->svflags & SVF_DEADMONSTER) && (trace.ent->client || (trace.ent->svflags & SVF_MONSTER)))
		{
			return NULL;
		}

		return g_edicts;
	}

	return NULL;
}

void
SV_CheckVelocity(edict_t *ent)
{
	if (!ent)
	{
		return;
	}
     
	if (VectorLength(ent->velocity) > sv_maxvelocity->value)
	{
		VectorNormalize(ent->velocity);
		VectorScale(ent->velocity, sv_maxvelocity->value, ent->velocity);
	}
}

/*
 * Runs thinking code for 
 * this frame if necessary
 */
qboolean
SV_RunThink(edict_t *ent)
{
	float thinktime;
      
	if (!ent)
	{
		return false;
	}
     
	thinktime = ent->nextthink;

	if (thinktime <= 0)
	{
		return true;
	}

	if (thinktime > level.time + 0.001)
	{
		return true;
	}

	ent->nextthink = 0;

	if (!ent->think)
	{
		gi.error("NULL ent->think");
	}

	ent->think(ent);

	return false;
}

/*
 * Two entities have touched, so
 * run their touch functions
 */
void
SV_Impact(edict_t *e1, trace_t *trace)
{
	edict_t *e2;
       
	if (!e1 || !trace)
	{
		return;
	}
     
	e2 = trace->ent;

	if (e1->touch && (e1->solid != SOLID_NOT))
	{
		e1->touch(e1, e2, &trace->plane, trace->surface);
	}

	if (e2->touch && (e2->solid != SOLID_NOT))
	{
		e2->touch(e2, e1, NULL, NULL);
	}
}

/*
 * Slide off of the impacting object
 * returns the blocked flags (1 = floor,
 * 2 = step / wall)
 */
int
ClipVelocity(vec3_t in, vec3_t normal, vec3_t out, float overbounce)
{
	float backoff;
	float change;
	int i, blocked;

	blocked = 0;

	if (normal[2] > 0)
	{
		blocked |= 1; /* floor */
	}

	if (!normal[2])
	{
		blocked |= 2; /* step */
	}

	backoff = DotProduct(in, normal) * overbounce;

	for (i = 0; i < 3; i++)
	{
		change = normal[i] * backoff;
		out[i] = in[i] - change;

		if ((out[i] > -STOP_EPSILON) && (out[i] < STOP_EPSILON))
		{
			out[i] = 0;
		}
	}

	return blocked;
}

/*
 * The basic solid body movement clip
 * that slides along multiple planes
 * Returns the clipflags if the velocity 
 * was modified (hit something solid)
 *
 * 1 = floor
 * 2 = wall / step
 * 4 = dead stop
 */
int
SV_FlyMove(edict_t *ent, float time, int mask)
{
	edict_t *hit;
	int bumpcount, numbumps;
	vec3_t dir;
	float d;
	int numplanes;
	vec3_t planes[MAX_CLIP_PLANES];
	vec3_t primal_velocity, original_velocity, new_velocity;
	int i, j;
	trace_t trace;
	vec3_t end;
	float time_left;
	int blocked;
                     
	if (!ent)
	{
		return 0;
	}
     
	numbumps = 4;

	blocked = 0;
	VectorCopy(ent->velocity, original_velocity);
	VectorCopy(ent->velocity, primal_velocity);
	numplanes = 0;

	time_left = time;

	ent->groundentity = NULL;

	for (bumpcount = 0; bumpcount < numbumps; bumpcount++)
	{
		for (i = 0; i < 3; i++)
		{
			end[i] = ent->s.origin[i] + time_left * ent->velocity[i];
		}

		trace = gi.trace(ent->s.origin, ent->mins, ent->maxs, end, ent, mask);

		if (trace.allsolid)
		{   
			/* entity is trapped in another solid */
			VectorCopy(vec3_origin, ent->velocity);
			return 3;
		}

		if (trace.fraction > 0)
		{   
			/* actually covered some distance */
			VectorCopy(trace.endpos, ent->s.origin);
			VectorCopy(ent->velocity, original_velocity);
			numplanes = 0;
		}

		if (trace.fraction == 1)
		{
			break; /* moved the entire distance */
		}

		hit = trace.ent;

		if (trace.plane.normal[2] > 0.7)
		{
			blocked |= 1; /* floor */

			if (hit->solid == SOLID_BSP)
			{
				ent->groundentity = hit;
				ent->groundentity_linkcount = hit->linkcount;
			}
		}

		if (!trace.plane.normal[2])
		{
			blocked |= 2; /* step */
		}

		/* run the impact function */
		SV_Impact(ent, &trace);

		if (!ent->inuse)
		{
			break; /* removed by the impact function */
		}

		time_left -= time_left * trace.fraction;

		/* cliped to another plane */
		if (numplanes >= MAX_CLIP_PLANES)
		{   
			/* this shouldn't really happen */
			VectorCopy(vec3_origin, ent->velocity);
			return 3;
		}

		VectorCopy(trace.plane.normal, planes[numplanes]);
		numplanes++;

		/* modify original_velocity so it
		   parallels all of the clip planes */
		for (i = 0; i < numplanes; i++)
		{
			ClipVelocity(original_velocity, planes[i], new_velocity, 1);

			for (j = 0; j < numplanes; j++)
			{
				if ((j != i) && !VectorCompare(planes[i], planes[j]))
				{
					if (DotProduct(new_velocity, planes[j]) < 0)
					{
						break; /* not ok */
					}
				}
			}

			if (j == numplanes)
			{
				break;
			}
		}

		if (i != numplanes)
		{   
			/* go along this plane */
			VectorCopy(new_velocity, ent->velocity);
		}
		else
		{
			/* go along the crease */
			if (numplanes != 2)
			{
				VectorCopy(vec3_origin, ent->velocity);
				return 7;
			}

			CrossProduct(planes[0], planes[1], dir);
			d = DotProduct(dir, ent->velocity);
			VectorScale(dir, d, ent->velocity);
		}

		/* if original velocity is against the original 
		   velocity, stop dead to avoid tiny occilations 
		   in sloping corners */
		if (DotProduct(ent->velocity, primal_velocity) <= 0)
		{
			VectorCopy(vec3_origin, ent->velocity);
			return blocked;
		}
	}

	return blocked;
}

void
SV_AddGravity(edict_t *ent)
{    
	if (!ent)
	{
		return;
	}
     
	ent->velocity[2] -= ent->gravity * sv_gravity->value * FRAMETIME;
}

/*
 * Returns the actual bounding box of a bmodel. 
 * This is a big improvement over what q2 normally
 * does with rotating bmodels - q2 sets absmin, 
 * absmax to a cube that will completely contain 
 * the bmodel at *any* rotation on *any* axis, whether
 * the bmodel can actually rotate to that angle or not.
 * This leads to a lot of false block tests in SV_Push
 * if another bmodel is in the vicinity.
 */
void
RealBoundingBox(edict_t *ent, vec3_t mins, vec3_t maxs)
{
	vec3_t forward, left, up, f1, l1, u1;
	vec3_t p[8];
	int i, j, k, j2, k4;

	for (k = 0; k < 2; k++)
	{
		k4 = k * 4;

		if (k)
		{
			p[k4][2] = ent->maxs[2];
		}
		else
		{
			p[k4][2] = ent->mins[2];
		}

		p[k4 + 1][2] = p[k4][2];
		p[k4 + 2][2] = p[k4][2];
		p[k4 + 3][2] = p[k4][2];

		for (j = 0; j < 2; j++)
		{
			j2 = j * 2;

			if (j)
			{
				p[j2 + k4][1] = ent->maxs[1];
			}
			else
			{
				p[j2 + k4][1] = ent->mins[1];
			}

			p[j2 + k4 + 1][1] = p[j2 + k4][1];

			for (i = 0; i < 2; i++)
			{
				if (i)
				{
					p[i + j2 + k4][0] = ent->maxs[0];
				}
				else
				{
					p[i + j2 + k4][0] = ent->mins[0];
				}
			}
		}
	}

	AngleVectors(ent->s.angles, forward, left, up);

	for (i = 0; i < 8; i++)
	{
		VectorScale(forward, p[i][0], f1);
		VectorScale(left, -p[i][1], l1);
		VectorScale(up, p[i][2], u1);
		VectorAdd(ent->s.origin, f1, p[i]);
		VectorAdd(p[i], l1, p[i]);
		VectorAdd(p[i], u1, p[i]);
	}

	VectorCopy(p[0], mins);
	VectorCopy(p[0], maxs);

	for (i = 1; i < 8; i++)
	{
		if (mins[0] > p[i][0])
		{
			mins[0] = p[i][0];
		}
         
		if (mins[1] > p[i][1])
		{
			mins[1] = p[i][1];
		}    
		
		if (mins[2] > p[i][2])
		{
			mins[2] = p[i][2];
		} 

		if (maxs[0] < p[i][0])
		{
			maxs[0] = p[i][0];
		}

 		if (maxs[1] < p[i][1])
		{
			maxs[1] = p[i][1];
		}
             
		if (maxs[2] < p[i][2])
		{
			maxs[2] = p[i][2];
		}
	}
}

/* ================================================================== */

/* PUSHMOVE */

/*
 * Does not change the entities velocity at all
 */
trace_t
SV_PushEntity(edict_t *ent, vec3_t push)
{
	trace_t trace;
	vec3_t start;
	vec3_t end;
	int mask;
                      
	VectorCopy(ent->s.origin, start);
	VectorAdd(start, push, end);

retry:

	if (ent->clipmask)
	{
		mask = ent->clipmask;
	}
	else
	{
		mask = MASK_SOLID;
	}

	trace = gi.trace(start, ent->mins, ent->maxs, end, ent, mask);

	if (trace.startsolid || trace.allsolid)
	{
		mask ^= CONTENTS_DEADMONSTER;
		trace = gi.trace (start, ent->mins, ent->maxs, end, ent, mask);
	}

	VectorCopy(trace.endpos, ent->s.origin);
	gi.linkentity(ent);

	if (trace.fraction != 1.0)
	{
		SV_Impact(ent, &trace);

		/* if the pushed entity went away 
		   and the pusher is still there */
		if (!trace.ent->inuse && ent->inuse)
		{
			/* move the pusher back and try again */
			VectorCopy(start, ent->s.origin);
			gi.linkentity(ent);
			goto retry;
		}
	}

	if (ent->inuse)
	{
		G_TouchTriggers(ent);
	}

	return trace;
}

typedef struct
{
	edict_t *ent;
	vec3_t origin;
	vec3_t angles;
	float deltayaw;
} pushed_t;

pushed_t pushed[MAX_EDICTS], *pushed_p;
edict_t *obstacle;

/*
 * Objects need to be moved back on a failed push,
 * otherwise riders would continue to slide.
 */
qboolean
SV_Push(edict_t *pusher, vec3_t move, vec3_t amove)
{
	int i, e;
	edict_t *check, *block;
	vec3_t mins, maxs;
	pushed_t *p;
	vec3_t org, org2, move2, forward, right, up;
	vec3_t realmins, realmaxs;
                    
	if (!pusher)
	{
		return false;
	}
     
	/* clamp the move to 1/8 units, so the position will
	   be accurate for client side prediction */
	for (i = 0; i < 3; i++)
	{
		float temp;
		temp = move[i] * 8.0;

		if (temp > 0.0)
		{
			temp += 0.5;
		}
		else
		{
			temp -= 0.5;
		}

		move[i] = 0.125 * (int)temp;
	}

	/* find the bounding box */
	for (i = 0; i < 3; i++)
	{
		mins[i] = pusher->absmin[i] + move[i];
		maxs[i] = pusher->absmax[i] + move[i];
	}

	/* we need this for pushing things later */
	VectorSubtract(vec3_origin, amove, org);
	AngleVectors(org, forward, right, up);

	/* save the pusher's original position */
	pushed_p->ent = pusher;
	VectorCopy(pusher->s.origin, pushed_p->origin);
	VectorCopy(pusher->s.angles, pushed_p->angles);

	if (pusher->client)
	{
		pushed_p->deltayaw = pusher->client->ps.pmove.delta_angles[YAW];
	}

	pushed_p++;

	/* move the pusher to it's final position */
	VectorAdd(pusher->s.origin, move, pusher->s.origin);
	VectorAdd(pusher->s.angles, amove, pusher->s.angles);
	gi.linkentity(pusher);

	/* Create a real bounding box for 
	   rotating brush models. */
	RealBoundingBox(pusher,realmins,realmaxs);

	/* see if any solid entities 
	   are inside the final position */
	check = g_edicts + 1;

	for (e = 1; e < globals.num_edicts; e++, check++)
	{
		if (!check->inuse)
		{
			continue;
		}

		if ((check->movetype == MOVETYPE_PUSH) ||
			(check->movetype == MOVETYPE_STOP) ||
			(check->movetype == MOVETYPE_NONE) ||
			(check->movetype == MOVETYPE_NOCLIP))
		{
			continue;
		}

		if (!check->area.prev)
		{
			continue; /* not linked in anywhere */
		}

		/* if the entity is standing on the pusher,
		   it will definitely be moved */
		if (check->groundentity != pusher)
		{
			/* see if the ent needs to be tested */
			if ((check->absmin[0] >= realmaxs[0]) ||
				(check->absmin[1] >= realmaxs[1]) ||
				(check->absmin[2] >= realmaxs[2]) ||
				(check->absmax[0] <= realmins[0]) ||
				(check->absmax[1] <= realmins[1]) ||
				(check->absmax[2] <= realmins[2]))
			{
				continue;
			}

			/* see if the ent's bbox is inside
			   the pusher's final position */
			if (!SV_TestEntityPosition(check))
			{
				continue;
			}
		}

		if ((pusher->movetype == MOVETYPE_PUSH) ||
			(check->groundentity == pusher))
		{
			/* move this entity */
			pushed_p->ent = check;
			VectorCopy(check->s.origin, pushed_p->origin);
			VectorCopy(check->s.angles, pushed_p->angles);
			pushed_p++;

			/* try moving the contacted entity */
			VectorAdd(check->s.origin, move, check->s.origin);

			if (check->client)
			{   
				check->client->ps.pmove.delta_angles[YAW] += amove[YAW];
			}

			/* figure movement due to the pusher's amove */
			VectorSubtract(check->s.origin, pusher->s.origin, org);
			org2[0] = DotProduct(org, forward);
			org2[1] = -DotProduct(org, right);
			org2[2] = DotProduct(org, up);
			VectorSubtract(org2, org, move2);
			VectorAdd(check->s.origin, move2, check->s.origin);

			/* may have pushed them off an edge */
			if (check->groundentity != pusher)
			{
				check->groundentity = NULL;
			}

			block = SV_TestEntityPosition(check);

			if (!block)

			{   /* pushed ok */
				gi.linkentity(check);
				continue;
			}

			/* if it is ok to leave in the old position, do it 
			   this is only relevent for riding entities, not
			   pushed */
			VectorSubtract(check->s.origin, move, check->s.origin);
			block = SV_TestEntityPosition(check);

			if (!block)
			{
				pushed_p--;
				continue;
			}
		}

		/* save off the obstacle so we can
		   call the block function */
		obstacle = check;

		/* move back any entities we already moved 
		   go backwards, so if the same entity was pushed 
		   twice, it goes back to the original position */
		for (p = pushed_p - 1; p >= pushed; p--)
		{
			VectorCopy(p->origin, p->ent->s.origin);
			VectorCopy(p->angles, p->ent->s.angles);

			if (p->ent->client)
			{
				p->ent->client->ps.pmove.delta_angles[YAW] = p->deltayaw;
			}

			gi.linkentity(p->ent);
		}

		return false;
	}

	/* see if anything we moved has touched a trigger */
	for (p = pushed_p - 1; p >= pushed; p--)
	{
		G_TouchTriggers(p->ent);
	}

	return true;
}

/*
 * Bmodel objects don't interact with each
 * other, but push all box objects
 */
void
SV_Physics_Pusher(edict_t *ent)
{
	vec3_t move, amove;
	edict_t *part, *mv;
                    
	if (!ent)
	{
		return;
	}
     
	/* if not a team captain, so movement
	   will be handled elsewhere */
	if (ent->flags & FL_TEAMSLAVE)
	{
		return;
	}

	/* make sure all team slaves can move before commiting 
	   any moves or calling any think functions if the move
	   is blocked, all moved objects will be backed out */
	pushed_p = pushed;

	for (part = ent; part; part = part->teamchain)
	{
		if (part->velocity[0] || part->velocity[1] || part->velocity[2] ||
			part->avelocity[0] || part->avelocity[1] || part->avelocity[2])
		{   
			/* object is moving */
			VectorScale(part->velocity, FRAMETIME, move);
			VectorScale(part->avelocity, FRAMETIME, amove);

			if (!SV_Push(part, move, amove))
			{
				break; /* move was blocked */
			}
		}
	}

	if (pushed_p > &pushed[MAX_EDICTS])
	{
		gi.error(ERR_FATAL, "pushed_p > &pushed[MAX_EDICTS], memory corrupted");
	}

	if (part)
	{
		/* the move failed, bump all nextthink
		   times and back out moves */
		for (mv = ent; mv; mv = mv->teamchain)
		{
			if (mv->nextthink > 0)
			{
				mv->nextthink += FRAMETIME;
			}
		}

		/* if the pusher has a "blocked" function, call it 
		   otherwise, just stay in place until the obstacle 
		   is gone */
		if (part->blocked)
		{
			part->blocked(part, obstacle);
		}
	}
	else
	{
		/* the move succeeded, so call all think functions */
		for (part = ent; part; part = part->teamchain)
		{
			SV_RunThink(part);
		}
	}
}

/* ================================================================== */

/*
 * Non moving objects can only think
 */
void
SV_Physics_None(edict_t *ent)
{                    
	if (!ent)
	{
		return;
	}
     
	/* regular thinking */
	SV_RunThink(ent);
}

/*
 * A moving object that doesn't obey physics
 */
void
SV_Physics_Noclip(edict_t *ent)
{                     
	if (!ent)
	{
		return;
	}
     
	/* regular thinking */
	if (!SV_RunThink(ent))
	{
		return;
	}

	VectorMA(ent->s.angles, FRAMETIME, ent->avelocity, ent->s.angles);
	VectorMA(ent->s.origin, FRAMETIME, ent->velocity, ent->s.origin);

	gi.linkentity(ent);
}

/* ================================================================== */

/* TOSS / BOUNCE */

/*
 * Toss, bounce, and fly movement. 
 * When onground, do nothing.
 */
void
SV_Physics_Toss(edict_t *ent)
{
	trace_t trace;
	vec3_t move;
	float backoff;
	edict_t *slave;
	qboolean wasinwater;
	qboolean isinwater;
	vec3_t old_origin;
                       
	if (!ent)
	{
		return;
	}
     
	/* regular thinking */
	SV_RunThink(ent);

	/* if not a team captain, so movement
	   will be handled elsewhere */
	if (ent->flags & FL_TEAMSLAVE)
	{
		return;
	}

	if (ent->velocity[2] > 0)
	{
		ent->groundentity = NULL;
	}

	/* check for the groundentity going away */
	if (ent->groundentity)
	{
		if (!ent->groundentity->inuse)
		{
			ent->groundentity = NULL;
		}
	}

	/* if onground, return without moving */
	if (ent->groundentity)
	{
		return;
	}

	VectorCopy(ent->s.origin, old_origin);

	SV_CheckVelocity(ent);

	/* add gravity */
	if ((ent->movetype != MOVETYPE_FLY) &&
		(ent->movetype != MOVETYPE_FLYMISSILE))
	{
		SV_AddGravity(ent);
	}

	/* move angles */
	VectorMA(ent->s.angles, FRAMETIME, ent->avelocity, ent->s.angles);

	/* move origin */
	VectorScale(ent->velocity, FRAMETIME, move);
	trace = SV_PushEntity(ent, move);

	if (!ent->inuse)
	{
		return;
	}

	if (trace.fraction < 1)
	{
		if (ent->movetype == MOVETYPE_BOUNCE)
		{
			backoff = 1.5;
		}
		else
		{
			backoff = 1;
		}

		ClipVelocity(ent->velocity, trace.plane.normal, ent->velocity, backoff);

		/* stop if on ground */
		if (trace.plane.normal[2] > 0.7)
		{
			if ((ent->velocity[2] < 60) || (ent->movetype != MOVETYPE_BOUNCE))
			{
				ent->groundentity = trace.ent;
				ent->groundentity_linkcount = trace.ent->linkcount;
				VectorCopy(vec3_origin, ent->velocity);
				VectorCopy(vec3_origin, ent->avelocity);
			}
		}
	}

	/* check for water transition */
	wasinwater = (ent->watertype & MASK_WATER);
	ent->watertype = gi.pointcontents(ent->s.origin);
	isinwater = ent->watertype & MASK_WATER;

	if (isinwater)
	{
		ent->waterlevel = 1;
	}
	else
	{
		ent->waterlevel = 0;
	}

	if (!wasinwater && isinwater)
	{
		gi.positioned_sound(old_origin, g_edicts, CHAN_AUTO,
				gi.soundindex("misc/h2ohit1.wav"), 1, 1, 0);
	}
	else if (wasinwater && !isinwater)
	{
		gi.positioned_sound(ent->s.origin, g_edicts, CHAN_AUTO,
				gi.soundindex("misc/h2ohit1.wav"), 1, 1, 0);
	}

	/* move teamslaves */
	for (slave = ent->teamchain; slave; slave = slave->teamchain)
	{
		VectorCopy(ent->s.origin, slave->s.origin);
		gi.linkentity(slave);
	}
}

/* ================================================================== */

/* STEPPING MOVEMENT */

/*
 * Monsters freefall when they don't have a ground 
 * entity, otherwise all movement is done with
 * discrete steps.
 *
 * This is also used for objects that have become
 * still on the ground, but  will fall if the floor
 * is pulled out from under them.
 */
void
SV_AddRotationalFriction(edict_t *ent)
{
	int n;
	float adjustment;
                        
	if (!ent)
	{
		return;
	}
     
	VectorMA(ent->s.angles, FRAMETIME, ent->avelocity, ent->s.angles);
	adjustment = FRAMETIME * STOPSPEED * FRICTION;

	for (n = 0; n < 3; n++)
	{
		if (ent->avelocity[n] > 0)
		{
			ent->avelocity[n] -= adjustment;

			if (ent->avelocity[n] < 0)
			{
				ent->avelocity[n] = 0;
			}
		}
		else
		{
			ent->avelocity[n] += adjustment;

			if (ent->avelocity[n] > 0)
			{
				ent->avelocity[n] = 0;
			}
		}
	}
}

void
SV_Physics_Step(edict_t *ent)
{
	qboolean wasonground;
	qboolean hitsound = false;
	float *vel;
	float speed, newspeed, control;
	float friction;
	edict_t *groundentity;
	int mask;
                         
	if (!ent)
	{
		return;
	}
     
	/* airborn monsters should always check for ground */
	if (!ent->groundentity)
	{
		M_CheckGround(ent);
	}

	groundentity = ent->groundentity;

	SV_CheckVelocity(ent);

	if (groundentity)
	{
		wasonground = true;
	}
	else
	{
		wasonground = false;
	}

	if (ent->avelocity[0] || ent->avelocity[1] || ent->avelocity[2])
	{
		SV_AddRotationalFriction(ent);
	}

	/* add gravity except: 
	     flying monsters 
	     swimming monsters who are in the water */
	if (!wasonground)
	{
		if (!(ent->flags & FL_FLY))
		{
			if (!((ent->flags & FL_SWIM) && (ent->waterlevel > 2)))
			{
				if (ent->velocity[2] < sv_gravity->value * -0.1)
				{
					hitsound = true;
				}

				if (ent->waterlevel == 0)
				{
					SV_AddGravity(ent);
				}
			}
		}
	}

	/* friction for flying monsters that have been given vertical velocity */
	if ((ent->flags & FL_FLY) && (ent->velocity[2] != 0))
	{
		speed = fabs(ent->velocity[2]);
		control = speed < STOPSPEED ? STOPSPEED : speed;
		friction = FRICTION / 3;
		newspeed = speed - (FRAMETIME * control * friction);

		if (newspeed < 0)
		{
			newspeed = 0;
		}

		newspeed /= speed;
		ent->velocity[2] *= newspeed;
	}

	/* friction for flying monsters that have been given vertical velocity */
	if ((ent->flags & FL_SWIM) && (ent->velocity[2] != 0))
	{
		speed = fabs(ent->velocity[2]);
		control = speed < STOPSPEED ? STOPSPEED : speed;
		newspeed = speed - (FRAMETIME * control * WATERFRICTION * ent->waterlevel);

		if (newspeed < 0)
		{
			newspeed = 0;
		}

		newspeed /= speed;
		ent->velocity[2] *= newspeed;
	}

	if (ent->velocity[2] || ent->velocity[1] || ent->velocity[0])
	{
		/* apply friction: let dead monsters who
		   aren't completely onground slide */
		if ((wasonground) || (ent->flags & (FL_SWIM | FL_FLY)))
		{
			if (!((ent->health <= 0.0) && !M_CheckBottom(ent)))
			{
				vel = ent->velocity;
				speed = sqrt(vel[0] * vel[0] + vel[1] * vel[1]);

				if (speed)
				{
					friction = FRICTION;

					control = speed < STOPSPEED ? STOPSPEED : speed;
					newspeed = speed - FRAMETIME * control * friction;

					if (newspeed < 0)
					{
						newspeed = 0;
					}

					newspeed /= speed;

					vel[0] *= newspeed;
					vel[1] *= newspeed;
				}
			}
		}

		if (ent->svflags & SVF_MONSTER)
		{
			mask = MASK_MONSTERSOLID;
		}
		else
		{
			mask = MASK_SOLID;
		}

		SV_FlyMove(ent, FRAMETIME, mask);

		gi.linkentity(ent);
		G_TouchTriggers(ent);

		if (!ent->inuse)
		{
			return;
		}

		if (ent->groundentity)
		{
			if (!wasonground)
			{
				if (hitsound)
				{
					gi.sound(ent, 0, gi.soundindex("world/land.wav"), 1, 1, 0);
				}
			}
		}
	}

	/* regular thinking */
	SV_RunThink(ent);
}

/* ================================================================== */

void
G_RunEntity(edict_t *ent)
{                         
	if (!ent)
	{
		return;
	}
     
	if (ent->prethink)
	{
		ent->prethink(ent);
	}

	switch ((int)ent->movetype)
	{
		case MOVETYPE_PUSH:
		case MOVETYPE_STOP:
			SV_Physics_Pusher(ent);
			break;
		case MOVETYPE_NONE:
			SV_Physics_None(ent);
			break;
		case MOVETYPE_NOCLIP:
			SV_Physics_Noclip(ent);
			break;
		case MOVETYPE_STEP:
			SV_Physics_Step(ent);
			break;
		case MOVETYPE_TOSS:
		case MOVETYPE_BOUNCE:
		case MOVETYPE_FLY:
		case MOVETYPE_FLYMISSILE:
			SV_Physics_Toss(ent);
			break;
		default:
			gi.error("SV_Physics: bad movetype %i", (int)ent->movetype);
	}
}

